In earlier years, storage tanks for liquids and particularly petroleum products such a gasoline consisted of large steel vessels that were buried in underground locations. Such tanks were well suited for their intended purpose when initially installed since the highly volatile contents were safely contained in a location were they were not readily subject to ignition by any external means which might otherwise cause a fire or explosion. However, after a number of years, such storage tanks would oftentimes deteriorate by reason of exposure to harsh environmental conditions.
When such deterioration would occur, the storage tank contents would leak from the tank at an unknown underground location. This would cause not only loss of the valuable contents, but also possible environmental contamination and the existence of a potentially hazardous condition. Equally important, ground water would leak into the underground tank causing a contamination of the liquid therein.
To overcome this problem, underground storage tanks have more recently been formed of various plastic materials that are less susceptible to deterioration. These tanks, when typically used for storing gasoline or other liquids, commonly have inner and outer walls spaced apart by a relatively great distance with the walls typically being reinforced by ribs therebetween, but such tanks have been undesirably large, heavy and require much more material for their construction. Moreover, ground water and/or gasoline may leak into the space between the inner and outer walls in the event of a defect in which case the leaking liquid will drain to the lower regions thereof.
With this dual-walled plastic construction, it is generally recognized that significant advances have been made over steel storage tanks in terms of long term avoidance of corrosion. It is nevertheless known that despite the advances to date, there is still a recurring problem of failure of the inner and/or outer walls of such storage tanks, not to mention transport and excavation problems. When this does occur in the field, the problem is serious due to the leakage of gasoline and/or ground water into the space between the two walls of the tank.
For this reason, it has been known to place sensors in the lower regions of the tank capable of providing warnings of leakage. This is, of course, desirable since it provides a warning of a most unsatisfactory condition and, furthermore, the sensors are such that the custodian of the tanks can actually tell whether the liquid leaking into the space between the walls is, for instance, ground water or gasoline. In such manner it is possible to know not only that there is a leak but also whether the leak is occurring in the inner or outer wall of the tank.
Unfortunately, such sensors do nothing toward eliminating the possibility of such leaks while also failing to provide a much more vital form of information to the custodian of the tank who is alerted to the existence of leakage between the walls. In particular, there has been no way to pinpoint the approximate location of the leak apart from whether it is in the inner or outer wall of the tank, and this has rendered repairs most time consuming and costly due to the need to search for the point of leakage before any repair can be made. In the case of the outer wall of the tank, this may require extensive excavation only after removal of large areas of concrete or asphalt covering the tank, which is obviously an undesirable undertaking.
The present invention is directed to overcoming one or more of the problems and accomplishing one or more of the objectives as aforementioned.